The present invention relates generally to direct-injection spark-ignition internal combustion engines, and more particularly to combustion control for direct-injection spark-ignition internal combustion engines in the presence of a request for rapid temperature rise of an exhaust purifier of the engine.
Japanese Patent No. 3325230 shows a technique for warming up an exhaust purifier of a direct-injection spark-ignition internal combustion engine when the exhaust purifier is not fully warmed up to its activation temperature. This technique employs split fuel injection during a period from intake stroke to ignition timing. The split fuel injection includes at least two fuel injection steps, i.e. a later fuel injection step carried out in the middle or later stage of compression stroke, e.g., from 120° BTDC to 45° BTDC (phase in crank angle before top dead center), to form an air-fuel mixture having local unevenness in air-fuel ratio in a combustion chamber, and an earlier fuel injection step carried out prior to the later fuel injection step to form an air-fuel mixture leaner than stoichiometric so that ignition of the later charge may initiate complete combustion of the earlier charge by flame propagation. During the split fuel injection, the ignition timing is retarded by a predetermined amount from an MBT (minimum advance for best torque) point. On the other hand, in a no-load engine operation region, the ignition timing is set to be before compression top dead center (TDC). In a low-speed and low-load engine operation region other than the no-load engine operation region, the ignition timing is retarded to be after compression TDC.